1. Field of the Invention
The present invention relates to a high frequency switch module that transmits and receives different kinds of communication signals, the number of which is equal to or higher than the number of antennas to be connected by a switch IC, and in particular, to a high frequency switch module including a multilayer substrate on which a switch IC is mounted.
2. Description of the Related Art
Conventionally, a variety of down-sized and multiband-compatible high frequency switch modules such as a configuration illustrated in Japanese Unexamined Patent Application Publication No. 2008-85775 have been designed for use in communication terminals. Typically, such a high frequency switch module includes a multilayer substrate in which conductors defining a circuit of the high frequency switch module are provided and a switch IC that is mounted on a top surface of the multilayer substrate.
The switch IC includes a common port and a plurality of switching ports, selects one of the plurality of switching ports, and connects a selected one to the common port. The switch IC is activated by applying a drive power signal (for example, a predetermined voltage Vd) from outside. The connection among the common port and the plurality of switching ports is selected depending on a combination of voltage levels of plural control signals (for example, three voltage types of the control signals, Vc1, Vc2, and Vc3). Since the switch IC is mounted on the top surface of the multilayer substrate, the conductors that supply the drive power signal and the control signals to the switch IC are provided inside the multilayer substrate. Further, these conductors are connected to lands on which the switch IC is mounted.
Further, conductors configured to transmit communication signals are provided inside the multilayer substrate.
However, in a conventional structure illustrated in Japanese Unexamined Patent Application Publication No. 2008-85775, the conductors for switch control, which transmit the drive power signal and the control signals (conductors transmitting direct voltages), tend to be arranged close to the conductors transmitting communication signals (conductors transmitting high frequency signals) if the multilayer substrate is to be reduced in size. When the conductors for switch control and the conductors transmitting communication signals are arranged close to each other, mutual interference tends to occur between the communication signal and the drive power signal or the control signals. For example, shortcomings, such as superimpositions of direct current voltages on the communication signals due to the drive power signal or the control signals or inverse superimpositions of high frequency noise on the drive power signal or the control signals due to the communication signals, tend to occur.